In a typical automobile engine power is transmitted from the engine crankshaft to one or more accessories using an endless polymeric belt. The belt may be driven by a driving sheave connected to the engine crankshaft and drive one or more driven sheaves connected to the accessories. The accessories may include, for example, an alternator, an alternator/generator/starter device, a compressor, or a power steering device.
A variety of belt tensioners have been proposed for maintaining the required tension in the power-transmitting belt to avoid belt slippage even during non-steady-state or transient conditions. For optimal function of a belt tensioner, it is desirable that the tensioner move quickly and easily toward the belt to take up slack but provide greater resistance to lifting of the tensioner away from the belt. This feature is desirable for proper control of steady state accessory torque loads that are occasionally interrupted with reverse transient load such as a wide-open-throttle one-two gear shift in a manual or automatic transmission. It is also desirable that the tensioner be lockable during certain operating conditions. For example, when the engine is cranking during start-up, accessory drive system resonance can occur that may cause excessive tensioner motion. During this condition it may be desirable to lock the tensioner solid until the engine reaches idle.
Accordingly, a new tensioner design having the aforementioned capabilities is desired.